Double bit assembly and method of using the same

ABSTRACT

A method to drill a hole in the soil by a bit assembly and a bit assembly comprising a ring-shaped bit (2) to drill the outer circle of the hole and to which a protection tube system (4), mounted in the hole while drilling, is coupled, and a cylindric inner bit (1) to drill the center portion of the hole, from which bit at least the rotative motion is transmitted to the outer bit (2). Drilling by the outer bit (2) and pulling out the protection tube (4) are disconnected upon need by reverse rotation of the inner bit, whereafter drilling is continued with the inner bit (1) only.

FIELD OF THE INVENTION

This invention relates to a method for drilling a hole in the soil andto a bit assembly and a drill bit for use in drilling a hole or tunnelin the soil.

BACKGROUND OF THE INVENTION

Previously known are, for instance from patent specifications FI 933074and GB 2 255 365, double bit assemblies where the inner bit that drillsthe center hole can be pulled out from the hole, while the ring bit thatdrills the outer hole circle is left in the bore. However, in theseexamples the inner bit can be pulled out from the hole after drillingand also reinstalled if drilling is continued.

On drilling a hole in the soil, the most general case is that the firstportion of the hole is made in soft soil, whereby a protection tube ispulled into the drilled hole. Eventually, on hitting rock, theprotection tube is not needed anymore. Drilling can then be continuedwithout a protection tube if change of the drilling procedure is easy. Aproblem arises when the drilling procedure is changed. The inner bitmust be pulled out from the hole and replaced by a bit that drills ahole with a smaller diameter. During this replacement, the completedrilling equipment is pulled out from the hole and reinstalled furnishedwith a new rock-drilling bit. This takes time and money, especially ifthe first bore in the soil is long.

SUMMARY OF THE INVENTION

By means of a method and bit assembly with a proper bit according tothis invention, a surprising improvement is achieved.

The advantage of this invention is that a hole requiring a protectiontube is drilled with the same bit assembly as a hole into rock. When theprotection tube is not needed, drilling proceeds nonstop with the innerbit only. In case drilling is stopped in a dead end, the inner bit canbe pulled out through the outer bit. Even the outer bit can be pulledout from the bore on condition that also the protection tube is alsopulled out simultaneously.

The bit assembly and the method can be applied to drilling by hammeringbut also to bits rotating only. The groove in the bayonet joint thatopens in both of the axial directions is favorably arranged as a flowchannel for flushing medium, whereas the joint is a simple construction.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention is disclosed with reference to theenclosed drawing, where

FIG. 1 shows a section of the bit assembly along line A--A.

FIG. 2 shows the bit assembly viewed from the front.

FIG. 3 shows the inner bit surface viewed from one side.

FIG. 4 shows a section of bore, where drilling proceeds by the inner bitonly.

FIG. 5 shows a cross-section of the ring bit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a section of the bit assembly including a cylindricinner bit 1 fastened to the head of hammer 7, a ring-shaped outer bit 2around the inner bit 1 and a protection tube 4 mounted in the hole whiledrilling and reaching the outer shell of outer bit 2. The inner bit 1and outer bit 2 are interconnected by a bayonet joint, where rotation istransmitted to the outer bit 2 by the inner bit 1. The inner bit 1 alsotransmits the hammer impacts to outer bit 2. Outer bit 2 pullsprotection tube 4 into the hole by means of the joint lap between them,which has restriction for the mutual axial motion.

FIG. 2 shows that in the circle between bits 1 and 2 three bayonetjoints are placed. In the inner bit 1 three axial grooves 6 are formedto run through the bit. Correspondingly, there are in outer bit 2 threeprojecting parts 3 with the same spacing which move in grooves 6.Sidewards from grooves 6 in inner bit 1 surface, as per FIG. 3, thereare notches for projecting parts 3, into which the projecting parts 3are guided due to the mutual rotation of the bits 1 and 2. Thereby, bits1 and 2 are in a locked state and bit 2 is rotated by bit 1, while thelocking is retained. The locking is opened by reverse rotation.Projecting parts 3 are square in order to receive the impacts from alarger surface area of the inner bit 1 and to transmit them to the outerbit 2. Groove 6 of inner bit 1 is also a flow channel for the flushingmedium, whose direction of flow, in this case, is backward in thechannel.

In FIG. 4 drilling has advanced to a location, where ring bit 2 andprotection tube 4 have been left. Drilling has proceeded only by bit 1.For demounting of the inner bit 1 from the outer bit 2, the rotation ofthe drill assembly has been reversed. Hammer 7 transmits the rotation toinner bit 1. Reverse rotation of inner bit 1 opens the bayonet joint insuch a way that projecting part 3 turns in groove 8 and enters groove 6.Thereafter, drilling further by reverse rotation, projecting parts 3glide out from grooves 6 to the front side of the ring bit, where thering bit 2 stops rotating and remains totally immobile. The inner bit 1drills rock or other hard ground that does not collapse into the hole.If drilling is stopped at a wanted depth or length, bit 1 and thedrilling equipment are pulled out from the hole. Bit 1 passes ring bit 2in running through it, when the bit 1 is turned into a position whereprojecting parts 3 hit grooves 6 and glide through bit 2.

FIG. 5 illustrates an example of ring bit 2 with several projectingparts 3 for several sequentially arranged axial bayonet joints, by meansof which construction a face to transmit impacts to ring bit 2 isproduced. Likewise, the protection tube 4 is pulled with severalsequential shoulder faces. On using many sequential bayonet joints andpulling shoulders of protection tube 4, it is possible to make ring bit2 thinner and yet strong enough for drillings of longer duration.

By means of a method and a bit assembly as per this invention it ispossible to carry out, advantageously, s.c. anchoring drilling, wheredrilling is done by the outer bit until rock is hit and a certaindistance by the inner bit in the rock. Since reversed flushing is usedfor removal of drill waste, whereby there is through inner bit 1 astraight channel tube up to the surface, an anchor wire rope can betaken through the channel to the bottom of the bore and, for instance,on pulling up the bit, concrete can be poured through the channel intothe hole. When the hole is filled and bit 1 pulled out to the level ofring bit 2, the outer bit 2 and even the protection tube 4 are thenpulled out and the hole is filled with concrete at the same time. Ifduring drilling the ring bit 2 and the protection tube 4 have been leftin the hole at too early a stage, the inner bit 1 can be pulled up tothe ring bit 2 and locked and drilling continued. In order to carry outproperly the mutual rotation of bits 1 and 2 necessary for locking, itis worth it to record on the ground the mutual depth position ofprotection tube 4 and the drill rod inside it, when bits 1 and 2 arelocked, so that relocking could be made in the same position. This is ofgreat significance, especially if there are several sequential bayonetlockings between the bits as shown in FIG. 5.

The inner bit 1 according to this invention includes transverse ringgrooves on its outer shell 8 ending in a vertical wall 9. The groove 8flanks function as faces transmitting impacts to ring bit 2 and the face9 as rotation-transmitting means. The outer shell of bit 1 lacks steppedimpact-transmitting shoulders known from previous designs.

By means of a method and bit assembly according to this invention bothvertical as well as horizontal holes can be drilled. Likewise, the axialgroove of the bayonet joint can also be in the ring bit 2 and theprojecting part in the inner bit 1.

I claim:
 1. An inner bit movable through either open end of a ring bitthat drills an outer circumference of a hole and securable to said ringbit to form a united bit assembly for drilling a hole or tunnel in soil,said inner bit including transverse grooves on an outer cylindricalsurface with respect to an axial direction, side faces of the groovesprotruding in a direction of a radius of the inner bit and transmittingimpacts and rotation to the ring bit.
 2. An inner bit according to claim1 further comprising axial grooves.
 3. An inner bit according to claim 1wherein the transverse grooves are sequentially arranged on the innerbit, the transverse grooves being open at one end and closed at anopposite end by an end face protruding in a direction of a radius of theinner bit.
 4. A method for drilling a hole in soil by means for a bitassembly comprising a ring-shaped outer drill bit for drilling an outercircumference of the hole, said outer bit being arranged to pull aprotection tube system into the hole when the drilling advances, acylindrical inner bit for drilling a center portion of the hole and alocking system comprising grooves and projecting parts, the projectingparts being located on one of a cylindrical inner surface of the outerbit and a cylindrical outer surface of the inner bit and the groovesbeing located in the other of the cylindrical inner surface of the outerbit and the cylindrical outer surface of the inner bit, said projectionsbeing movable into said grooves for locking said inner and outer bitsand movable out of said grooves to allow transverse movement betweensaid inner and outer bits, rotative motion of said bit assembly beingtransmitted from said inner bit to said outer bit by means of saidlocking system, said method comprising the steps of:locking said innerand outer bits; drilling by means of the outer bit and pulling of theprotection tube; disconnecting the outer bit from the inner bit at adesired drilling depth; and continuing drilling with said inner bitonly.
 5. A method according to claim 4, wherein, during said step ofdrilling by means of said outer bit, the inner bit transmits impacts tothe outer bit by means of said projecting parts.
 6. A method accordingto claim 4, wherein, when said inner bit and said outer bit are unlockedduring said step of disconnecting, the inner bit is movable through theouter bit in forward and backward transverse directions and, upon need,the outer bit is lockable to the inner bit.
 7. A method according toclaim 4, wherein a first portion of a hole is drilled during the step ofdrilling by the locked inner and outer bits, and a second portion of thehole is drilled by the inner bit during said step of continuingdrilling, said method further comprising the step of removing the innerbit from the hole either alone or together with the outer bit and theprotection tube.
 8. A bit assembly including:an inner bit for drilling acenter of a hole; an outer bit for drilling an outer circumference ofsaid hole, the inner bit being threaded through the outer bit; aprotection tube mounted in said hole during drilling and coupled to saidouter bit; and a rotation-transmitting joint between said inner andouter bits, the joint including a locking system comprising grooves andprojecting parts, the projecting parts being located on one of acylindrical inner surface of the outer bit and a cylindrical outersurface of the inner bit, and grooves being located in the other of thecylindrical inner surface of the outer bit and the cylindrical outersurface of the inner bit, the projecting parts being movable into saidgrooves for locking said inner and outer bits to allow drilling by saidouter bit and movable out of said grooves to allow movement of saidinner bit out of said outer bit to allow drilling by said inner bitonly.
 9. A bit assembly according to claim 8, wherein the locking systemcomprises one or more sequential bayonet joints between the inner bitand the outer bit for transmitting rotative motion and drilling forcefrom the inner bit to the outer bit.
 10. A bit assembly according toclaim 8, wherein one of the grooves extending in an axial direction inone of the inner and outer bits comprises a flow channel for flushingmedium.
 11. The bit assembly according to claim 8, wherein said groovesare located in the inner bit and the projecting parts are located in theouter bit.